More than 140 schoolchildren are being 'brainwashed' into becoming suicide bombers for Islamist militants after being kidnapped in Syria, it emerged today.

The Kurdish pupils, aged between 14 and 16, are being held hostage in the ISIS-controlled city of Manbij, where they are being forced to take lessons in radical Islamic theology.

One 15-year-old boy, known as Mohammed, said masked fighters made him watch a video of fighters beheading a man on their first day - then warned he would face the same fate if he tried to escape.

'Brainwashed': Some of the 140 schoolboys reportedly captured by ISIS militants in Syria while travelling back home on a convoy of buses after taking their final exams in the city of Aleppo

Snatched: The Kurdish pupils, aged between 14 and 16, are being held hostage in the ISIS-controlled city of Manbij, where they are being forced to take lessons in radical Islamic theology

He said the men, armed with AK-47 machine guns, told him: 'This is jihad for the sake of God.'

Despite the barbaric threat, he and a friend managed to escape after creating a diversion, climbing a fence and running to safety.

His account comes days after a human rights group revealed how ISIS militants waging war in Iraq and Syria are recruiting children for roles ranging from soldiers and snipers to stretcher bearers and suicide bombers.

He was among more than 140 Kurdish schoolboys kidnapped in Syria last month by ISIS, according to the Syrian Observatory for Human Rights and local activists.

The children were then taken to a mosque in Manbij, handed blankets and forced to sleep in a single rooms with 17 boys in each one.

They are woken up at dawn each day for prayer, made to take lessons for several hours on Sharia law then forced to watch horrific videos of executions and suicide missions, he said.

A father of one of the captured pupils, who is a senior Kurdish leader but didn't want to be identified in fear for his son's safety, said: 'They are trying to brainwash them.

'We have raised our children well, but we are worried how this will affect them psychologically.'

Show of strength: ISIS parade in a commandeered Iraqi security forces vehicle down a main road at the northern city of Mosul, which the militants captured at the start of their insurgency in Iraq two weeks ago

Earlier this week, a report by Human Rights Watch revealed how rebel groups across the ideological spectrum have employed children in the civil war in Syria.

Military and police forces in Kurdish-controlled areas have also used teenagers, it said.

'Syrian armed groups shouldn't prey on vulnerable children — who have seen their relatives killed, schools shelled and communities destroyed — by enlisting them in their forces,' said Priyanka Motaparthy, the author of the 31-page report.

'The horrors of Syria's armed conflict are only made worse by throwing children into the front lines.'

Human Rights Watch said the extremist Nusra Front and the Islamic State have both targeted children as young as 15 through education programs, which include military training.

The group, which said the number of children fighting in the conflict is unknown, based its report on interviews with 25 children and former child soldiers in Syria.